The present invention relates to a process and apparatus for providing monitoring of the efficiency of operation of an EDM machine by way of a visual display of a measured electrical magnitude proportional to the current flow at the machining gap accomplishing useful work or, in the alternative, providing an analog indication of the actual material removal rate in the course of a machining operation.
It is known in EDM technology to provide an indication of machining efficiency by measuring magnitudes representative of the duration of the electrical discharges at the gap between an electrode tool and an electrode workpiece, or the current or voltage level of the electrical discharges. For example, U.S. Pat. No. 3,474,216 discloses a circuit for comparing the number of useful electrical discharges to a predetermined number of successive electrical discharges applied to an EDM machining gap, and for providing a magnitude representative of the ratio of those two numbers. The ratio represents the rate of useful electrical discharges or, in other words, the quality of the electrical discharges, but it does not provide any indication with respect to the useful machining current or the real machining rate, because the ratio does not take into consideration the density of the electrical discharges during the time interval during which they are counted.
Another circuit, disclosed in U.S. Pat. No. 3,816,692, determines the product of the pulse rate at the gap during a predetermined time interval by the current rate through the gap during the same time interval and supplies a digital display of the product. Such a circuit permits to obtain some indications of the electrical discharge rate, but it does not permit to appraise the useful machining current because it takes into consideration both the machining discharges and the non-machining discharges such as arcing and short-circuits, the frequency of the non-machining discharges having a non-negligible influence upon the useful current and the machining efficiency. Another portion of the disclosed circuit provides a visual display of the number of abnormal discharges taking place during a predetermined machining time interval. The machine operator is not able to derive from the two informations thus provided the real value of the useful machining current.
The present invention has for an object to remedy the shortcomings and inconveniences of those prior art circuits by supplying to the machine operator a continuous information display of the useful machining current.